Y. Song, Z. Zhuang, H. Li, Q. Zhao, J. Li, W. Lee, and C. Giles. Proceedings of the 31st annual international ACM SIGIR conference on Research and development in information retrieval, page 515--522. New York, NY, USA, ACM, (2008)
L. Gou, H. Chen, J. Kim, X. Zhang, and C. Giles. Proceedings of the 19th International Conference on World Wide Web, page 1103--1104. New York, NY, USA, ACM, (2010)